Method and apparatus for drying



Dec. 6, t1938. J. G. ADINWIDDIE 2,139,445

METHOD AND APPARATUS FOR DRYING Filed Oct. 15,-1936 .Y d .A 51395445@ METHOD APPARATUS Fon name 7 Joseph G. Dinwiddie, Waynesboro, ya., assig'nor ,to E. I. du Pont de Nemours &`Compan'y, Wil- 'L n, Del., a 'corporation of Delaware i application ombel- 15,1936, serial No. 105,741,

This invention 5relates toa method and appato be denuded of moistmaterial, thus allowing J ratus for drying coarsely or finely divided matedrying `medium to be drawn thru the "denuded lrials, such as by means of a continuous rotary areas of the support without contacting the moist .vacuum drum drier. .More particularly, it r-'ematerial and without therefore exertinganysub-j lates toa method and apparatusfor drying mastantial drying' effect. f 4

terials containing arelatively small proportion of In order to arrive at a better understanding liquid. g ofthe inven ion, reference is had to ther follow- In a continuousy rotary vacuum drier, an ing descripti n taken i'n connection with the ac- Y enclosed ,drum is continuously rotated and vaccompanying drawing. It is tobe understood that 91h' ullm is applied tothe interior side' of a screen or this description illustrative and not limitative. lo pervious fabric support covering the outer drum' In thedrawing, Fig; 1 is a cross-sectional side periphery and carrying on its exterior sidethe view'of a rotary vacuum drum drier in accordmaterial to be dried The material to be dried ance with this invention; Fig. 2 is a `front view of is supplied to the screen or other support in a Vthe knife spreader or doctor knife 4 in combina- 15 -leeulated manner, such as by a hopper or star tion with the Vscreen covered vacuum drum 3. '15 wheel feed devicegenerally positioned above the Referring to the drawing, moist material, such drum.' The material is'spread to auniform layer as granular cellulose acetate, havingra moisture Aof. desirable thickness by means of a doctor knife. content 'of 2li-50%, is. dropped through a hopper A'heated gaseous drying medium such as air, l into a rotatingstar'wheel feed devicegll that 2() supplied by'fans lsituatedon oppositesidesof the regulates the amount of material admitted .to a o drum drier, is drawn through the layerof the feedchamber' I0 and on toa screen support '2 I v "material to be dried by theY aforementioned vac covering the peripheryof a drum; supported on umn.. After thednrmhasrotated approximately stationary shaft 23 and slowly rotating in the 180 degrees, the material is' sufficiently dry to be direction of the arrow, such as by means ofdrive '25 discharged into a'hopperjfor suitable disposal. flange 21 and belt drive 28. The rotatio'nof th'e 25 Thecontinuous rotary vacuum drum drier is drum carries the deposited material 22 past a particularly eiective'indrying crystalline matevdoctor knife 4, adjustable to' yield across the j rlals, such as -sodium Y bicarbonate, entire width of the periphery of the drum a layer phosphate, and -ammcniumsulfate or granular of material Aapproaching a rmiform thickness of .o materials, such-as cellulose acetate, and many 1' to 1%", to a'dryingchamber II. During the ab other materialsin' a wide diversity of industries.` rotation of the drum 3 through the 'arc A to B, a f

This time 0f drier.. however. has the disadvanf' vacuum vof 8" to 15" of-water is applied on the me of a low unit capacity' Perunit of heated interior 'of thetdrum. lThematerial 22 is dried air employed in drying, particular1y when em- Vby passage of heated air. drawn inward through 35 ployed for the drying of materials containing la the layer of material bythe vacuum. 'I'he heat $5 I relatlvely'small proportion-of liquid. This disedair is supplied through theducts i and 6 by advantagehasbeen a prime Vfactorin retarding means'of the fans jand I6. During the rota- .1' the extensive adaptation'by the industries of the tion of the drumthrough the arc' B to C, a blast" rotary vacuumdnimdrier that Otherwise Well del'oi air or the like isapplied onl the interiorof w Serv'edthe 'most IBVOlble recOgnitiom the drum lin order to 'assist the discharge of` n *It is therefore. an objectl of this inventiOn t0' the driedA material through the hopper V8 into increase the unit capacity of! a drier such as & bags,- storage bins, or other suitable collecting f'l'otly Vacuum .dlil Der unit Pf hetd Bil' means. Nopressure or 'vacuum is exerted onthe- .employell y interior of thedrurnlduring its'rotation through l. It is another object ofthe'present invention vthe are cionlto secures. continuous'layero'i' material to be' 1f, wm be unda-8M 1mm-se, that-rotary.

across the entirzwidth 0f?. SllDiOl't-ill` 8 vacuum drum drying ispreferably a 001115111110115 i rotary vacuum drummeri procedure 'and that the operations of charging,

' Other objects will be evident in the descripdrying, and discharging the material neemglml.' tion 0f the inventill, given' hereinafter, y taneously. Among other ways. this may'be ac, 50 These Objects are accomplished, generally. by complishedV asfollows: The interior of 'the voidins eXSSiVe eddy Currents 0f 28889118 dryis-'divlded'into compartments Il', each comparting. medium in the vicinity' of the moist material 'ment having ajscreen support4 2l at one .end and to bedr-led.v I hcave found that vthe presence of the other end 2! communicating by holes or other" .sucheddy currents causes areas of the support suitable es Il with the interlor of a partly.

hollow stationary shaft 23 similarly provided with holes or other suitable passages. 'I'he interior o f the shaft 23 is divided into two closed compartments 3| and 32 communicating directly with compartments 30. Vacuum is continuously applied to compartment 3| by means of vacuumpipe 34, and pressure continuously appliedto compartment 32 by means ofpressure pipe 35. In this wayit is seen that vacuum is applied to some compartments 30 and pressure to others, so that vacuum is exerted on the screen support situated in the arc A to B and pressure on the screen support situated in the arc B to C. As the drum rotates, some compartments 30 move out of registry with compartment 3| and into registry with compartment 32, andare replaced by other compartments 30 soA thatsthe pressure and vacuum are maintained sectionalized. -In order to vprevent both vacuum and pressure being applied at the same time to any one of the compartments 30,

compartments 3| and 32 are divided'by a wall 36 having a thick exterior portion 31 having a length of arc equal to or greater than the greatest length of arc of end 29 of any compartment 30.

Prior tothe present invention, the feed chapiber I0 consisted of a sealed compartment separated from the drying chamber by the solid, exible baffle 9 held in contact with the screen support 2| of the drum 3, s uch as by meansjof a. spring I8, by a solid doctor knife corresponding to knife 4 spaced approximately 1'f to 11/2" from the screen support 2| and bythe mass of material 22 admitted through the star feed wheel I4. .The

application of vacuum to thevscreen support 2| through the vacuum compartment 3| built up, therefore, a considerable vacuum` in the feed chamber I0. On the other hand, the heated air supplied by the fans I5 and I6 'maintained the drying chamber at substantially atmospheric pressure. As a result, there existed between the chambers I0 and a substantial differential pressure that engendered a more or less violent infux of air through the space between the doctor knife.

substituting for the solid doctor knife hitherto employed a doctor knife. 4 having perforations 4 of a suitable size and number to maintain the rpressure in the chambers Il and substantially equal, or at least sufficiently equal so that n o disturbing air currents are drawn through the space between the doctor knife and the screen support 2|.

It will be recognized, of course. by those ,skilledv in the art of drying materials that the preferred embodiment is susceptible to considerable modification without departure from the fundamentals of the invention. Thus, the holes allowing ingress of heated air into the chamber I0 need not necessarily be placed on the doctor knife but may instead be located atany suitable position in the chamber Ill. Alternatively, the baille 9 maybe perforated with holes of suitable size and shape and inclined at such an angle to the rotary drum surface that the holes do not readily become clogged with material and that heated .air from the duct 6 readily passes into the chamber I0. While in general the elimination of any differential pressire between the chambers I0 and probably represents the optimum operating-conv. r'15% or 50% Water.

even' desirable to maintain a difference of pres-.

`sure between chambers I0 and of 2 of water, or even up to 3". In no case, however, should the difference of pressure be sucient to induce air currents of enough magnitude to create channeling of the material on the screen support.

The invention is most applicable to materials which, as supplied to the rotary vacuum dryer, contain a relatively small proportion of liquid, such as less than water, and usually less than Such materials are peculiarly subject to channeling, while materials containing more than 90% liquid tend to mat down and cohere to a sufficient extent to avoid the disrupting influence of eddy currents of air. Among the materials which may be suitably dried by this invention may be mentioned `granularand crystalline materials, such as flake and vacuum pan salt, sodium bicarbonate, trisodium phosphate, and ammonium sulfate; metallurgical and quarry' products such as building and phosphate sand; and light but free filtering v materials such as ground regenerated cellulose film, cotton linters, and cotton seed meal. f

The present invention has contributed considerably to the art of drying materials by increasing to a notable extent the efiiciency and capacity of the rotary vacuum drum drier. Maintaining al1 other conditions such as temperature of the heatled air, degree of vacuum, size of particles, size of the rotary drum, etc., the same, the use of this invention has increased the capacity of the rotary vacuum drier 50-75% or more. The increased capacity lowers the expense of drying and should promote more extensive adaptation of this type 'of equipment for a wide diversity of products throughout many industries. It is now possible to dry certain products by rotary vacuum drum drying that have never before been economically dried by this process. As to products that have previously been dried advantageously on a rotary vacuum drum drier, the invention should result in a reduction of the cost of production that will render the products more readily available to the public. 4

Any variation `or modification of the invention as described, which. conforms to the spirit of the invention, is intended to be included within the scope of the claims.

I claim:

1. An apparatus for drying material comprising a feed chamber, means for feeding to said chamber material to be dried, a movable support within saidchamber, means for applying vacuum to 'the opposite side of said support, a regulating device for regulatingv the thickness of material to Ybe dried on said support, said regulating device forming one boundary of said chamber, said Support being adapted to move past said yregulating device, a drying chamber on the opposite side of said regulating device from said feed chamber, means for' supplying fluid drying medium to said drying chamber, and passages communicating between said drying chamber and said feed chamber for maintaining the pressure on opposite sides of said regulating device substantially equal. Y

2. An apparatus for drying material comprising a feed chamber, means for feeding to said chamber material to be dried, a movable support within said chamber, means for yapplying vacuum to the opposite side of saidsupport, al doctor knife forming one boundary of said chamber, said support being adapted to move past saidl doctor said doctor -knife from said feed chamber, means for supplying heated air to said drying chamber,`

and openings in said doctor knife for the passage of air between saidY drying'chamber and said feed chamber for .maintaining the pressure on opposite sides of saidv regulating device substan- 3. The process of suction drying of materials which comprises depositing the wet materials to be dried on the perforated surface of a drying element in a substantially enclosed depositing zonein which the side of the element opposite that on which the material is being deposited is maintained at a pressure substantially less than atmospheric, moving said drying element past a device for regulating the thickness of materials thereon into a zone in which the-side of the drying element containing the Vmaterial is supplied 'with a gaseous `drying medium having an elevated temperature and the opposite side of the element is maintained at a pressure substan- Itially less than atmospheric, and passing gaseous drying medium to said depositing zone ata point lspaced from the surface of the deposited material, and maintaining ithe pressure of gaseous drying medium in the depositing zone substantially equal to the pressure in the-drying zone whereby. to prevent movement of the gaseous drying medium from the drying zoe to the depositing zone past the surface-'ofthe deposited material. p

, JOSEPH G. .DINWIDDIE 

